1. Field of the Invention
The present invention relates to a heat processing apparatus for heat-processing matters such as semiconductor wafers while keeping them uniformly heated.
2. Description of the Related Art
There are usually well-known the heat processing apparatuses intended to apply a predetermined heat process to matters such as semiconductor wafers while keeping them uniformly heated, to thereby form thin film or diffuse heat on each of the semiconductor wafers.
One of the heat processing apparatuses of this kind is disclosed by Japanese Utility Model Disclosure Hei 1 - 122064. In the case of this heat processing apparatus, a seal section for the process tube is located adjacent to the open bottom of the heating furnace and an O-ring made of elastic material is set at this seal section. A lower flange of the seal section holding the O-ring is water-cooled and the ring-shaped outward projection of the process tube which is contacted with the O-ring is covered by an upper water-cooled flange of the seal section. The O-ring is made of elastic material having a heat resistance of 200.degree. C., and the heat of the O-ring is cooled by the upper and lower water-cooled flanges.
When the heating furnace is heated to a high temperature of 1000.degree. C., however, the lower portion of the O-ring which is contacted with the lower water-cooled flange can be kept 50.degree. C., for example, but the upper portion thereof is heated higher than 200.degree. C. by light radiated from the heating furnace and passed through the quartz-made process tube because the heat conductivity of the O-ring is low.
The ring-shaped outward projection of the process tube which is contacted with the upper portion of the O-ring is covered by the upper water-cooled flange and a heat transmitting Teflon packing is sandwiched between the upper flange and the ring-shaped outward projection of the process tube. When the process tube is exhausted vacuum, however, a clearance is created between the Teflon packing and the upper flange to stop heat conduction. As the result, the upper portion of the O-ring is heated higher than 200.degree. C. and thus heat-dissolved. The O-ring cannot achieve sufficient sealing effect accordingly. In order to protect the O-ring from heat, however, the O-ring seal section must be located sufficiently remote from the heating furnace. This makes the heat processing apparatus large in size.
In the case of another heat processing apparatus disclosed in Japanese Utility Model Disclosure Sho 62 - 92635, the projected portion of a water-cooled cap is attached to the inside of the process tube which is contacted with the O-ring so as to cover the O-ring by the cap.
The O-ring in this apparatus can be sufficiently water-cooled because the projected portion of the water-cooled cap is inserted into the process tube. However, process gas used to form film on each semiconductor wafer is also cooled by the projected portion of the water-cooled cap inserted inside the process tube.
When SiH.sub.2 Cl.sub.2 and NH.sub.3 gases are introduced into the process tube to form film on each semiconductor wafer according to the CVD, therefore, film, easy to peel off, adheres to the projected portion of the cap because the temperature of this cap projection is low. Or powder product (or antimony chloride) adheres to it when its temperature is lower than 120.degree. C. As the adhering film becomes thick or every time the process tube is opened and closed, the film or product peels off the cap and floats in the process tube to adhere to the wafers. The wafers are thus contaminated to thereby reduce the productivity of wafers.